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COPYRIGHT 2006 Wilson Ornithological Society
The Loggerhead Shrike (Lanius ludovicianus) is of conservation interest throughout its range, and has been designated a "Bird of Conservation Concern" (U.S. Fish and Wildlife Service 2002). The range of the species has contracted greatly over the past half-century (Cade and Woods 1997), and Christmas Bird Count and Breeding Bird Survey data indicate a continent-wide decrease in abundance. The sharpest declines have occurred in the core of the shrike's range in southern and Gulf Coast areas (Yosef 1996).
Most studies of Loggerhead Shrikes have revealed high nest success (mean of 56%; Yosef 1996, Esely and Bollinger 2001), suggesting that problems associated with winter habitat and survival may be causes for population declines (Haas and Sloane 1989, Brooks and Temple 1990, Gawlik and Bildstein 1993). Based on reports of high nest success throughout the species' range, Maddox and Robinson (2004) considered it fortuitous that habitat degradation had not resulted in elevated rates of nest predation or decreased productivity. Our observations, and the results of some, more recent studies (DeGeus 1990, Yosef 1994, Collins 1996, Esely and Bollinger 2001), suggest there are landscapes and nest-site contexts in which this presumption does not apply. Our objectives were to measure nest success of Loggerhead Shrikes in a region of intensive agriculture with marginal habitat, and to determine whether land use near nests, or nest-site context, influenced nest fate.
METHODS
From 1998 through 2000, we monitored Loggerhead Shrike nests within a 125-[km.sup.2] area of southern Jasper County, Illinois. The study was centered on Prairie Ridge State Natural Area (88[degrees] 12' W, 38[degrees] 57' N) and included most of Smallwood Township and adjacent portions of Wade and Fox townships. Jasper County's landscape is composed of 71% row crop (corn, Zea mays; and soybeans, Glycine max), 6% wheat (Triticum aestivum; most double-cropped to soybeans after harvest), 6% rural grassland (hay, pasture, roadsides, and idle grass), 13% woodland, and 1% roads, residential/urban areas, and small amounts of open water and other land covers (Illinois Interagency Landscape Classification Project 2002). Our study area differed from the county as a whole by having greater row crop cover (>85%) and less woodland cover (<5%; JWW unpubl, data).
Between 1966 and 2000, North American Breeding Bird Survey results suggested declining abundance of Loggerhead Shrikes in Illinois (-4.5%/year) and the Midwest (-0.3%/year in the eight states of U.S. Fish and Wildlife Service Region 3; Sauer et al. 2005). From 1994 to 1996, roadside searches within 49 [km.sup.2] of the center of our 1998-2000 study area documented 12 (1996) to 16 (1994) shrike territories annually (roughly 0.25-0.33 shrike territories/[km.sup.2]; JWW unpubl, data, reported to the Illinois Department of Natural Resource's Natural Heritage database). During our 1998-2000 study, the densities of nesting shrikes were similar to, or lower than, that reported during the 1994 to 1996 roadside surveys.
From March through June, we located...
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